Method configuration to access sample attribute values in sample set

I am configuring a method for a sample set.

In my data model, my samples have an attribute called clean_results_file, and I would like to access these attribute values for all samples in a sample set. I have the following WDL which works with Cromwell with a file (my_cleanfiles) that lists each input clean_result_file.

Root entity type: sample_set

    workflow workflowmeta {

    File my_cleanfiles

    Array[File] cleanfiles = read_lines(my_cleanfiles)

    ...

What is the appropriate way get the Array[File] cleanfiles to contain the clean_result_files attribute in FireCloud?

I was trying "workflowmeta.my_cleanfiles: (File) this.samples.clean_results_file" Does this method configuration create an Array[File]?

Thanks,
Alisa